BACKGROUND OF THE INVENTION
Field of the Invention
[0001] Embodiments of the invention generally relate to the field of semiconductor manufacturing
processes and devices, more particularly, to methods of depositing silicon-containing
films for forming semiconductor devices.
Description of the Related Art
[0002] Size reduction of metal-oxide-semiconductor field-effect transistors (MOSFET) has
enabled the continued improvement in speed performance, density, and cost per unit
function of integrated circuits. One way to improve transistor performance is through
application of stress to the transistor channel region. Stress distorts (e.g., strains)
the semiconductor crystal lattice, and the distortion, in turn, affects the band alignment
and charge transport properties of the semiconductor. By controlling the magnitude
of stress in a finished device, manufacturers can increase carrier mobility and improve
device performance. There are several existing approaches of introducing stress into
the transistor channel region.
[0003] One such approach of introducing stress into the transistor channel region is to
incorporate carbon into the region during the formation of the region. The carbon
present in the region affects the semiconductor crystal lattice and thereby induces
stress. However, the quality of epitaxially-deposited films decreases as carbon concentration
within the film increases. Thus, there is a limit to the amount of tensile stress
which can be induced before film quality becomes unacceptable.
[0004] Generally, carbon concentrations above about 1 atomic percent seriously reduce film
quality and increase the probability of film growth issues. For example, film growth
issues such as undesired polycrystalline or amorphous silicon growth, instead of epitaxial
growth, may occur due to the presence of carbon concentrations greater than 1 atomic
percent. Therefore, the benefits that can be gained by increasing the tensile stress
of a film through carbon incorporation are limited to films having carbon concentrations
of 1 atomic percent or less. Moreover, even films which contain less than 1 atomic
percent carbon still experience some film quality issues.
US 2003/045063 A1 describes a semiconductor device and a method for manufacturing the same.
JP H10 41321 A refers to a manufacturing method of a bipolar transistor.
US 5 607 724 A relates to a process for depositing undoped or doped silicon at high growth rates.
In particular,
US 5 607 724 A describes a method of forming a phosphorus doped silicon film by providing a mixture
of silane and phosphine gases in a hydrogen carrier gas, so as to form a silicon film
containing about 1.5 × 10
21 cm
-3 of phosphorus.
[0005] Therefore, there is a need for producing a high tensile stress epitaxial film which
is substantially free of carbon.
SUMMARY OF THE INVENTION
[0006] Embodiments of the present invention generally relate to methods for forming silicon
epitaxial layers on semiconductor devices. A method according to the invention is
defined in claim 1. Advantageous embodiments are set out in the dependent claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] So that the manner in which the above recited features of the present invention can
be understood in detail, a more particular description of the invention, briefly summarized
above, may be had by reference to embodiments, some of which are illustrated in the
appended drawings. It is to be noted, however, that the appended drawings illustrate
only typical embodiments of this invention and are therefore not to be considered
limiting of its scope, for the invention may admit to other equally effective embodiments.
Figure 1 is a flow chart illustrating a method of forming a phosphorus- containing
silicon epitaxial layer.
Figure 2 is a graph illustrating the dopant profile of a film formed according to
embodiments of the invention.
Figure 3 is a graph illustrating the tensile stress of the film of Figure 2.
[0008] To facilitate understanding, identical reference numerals have been used, where possible,
to designate identical elements that are common to the figures. It is contemplated
that elements disclosed in one embodiment may be beneficially utilized on other embodiments
without specific recitation.
DETAILED DESCRIPTION
[0009] Embodiments of the present invention generally relate to methods for forming silicon
epitaxial layers on semiconductor devices as defined in claim 1. The methods include
forming a silicon epitaxial layer on a substrate at increased pressure and reduced
temperature. The silicon epitaxial layer has a phosphorus concentration of about 1
×10
21 atoms per cubic centimeter or greater, and is formed without the addition of carbon.
A phosphorus concentration of about 1 ×10
21 atoms per cubic centimeter or greater increases the tensile strain of the deposited
layer, and thus, improves channel mobility. Since the epitaxial layer is substantially
free of carbon, the epitaxial layer does not suffer from film formation and quality
issues commonly associated with carbon-containing epitaxial layers. Substantially
free of carbon as used herein refers to a film which is formed without the use of
a carbon-containing precursor; however, it is contemplated that trace amounts of carbon
may be present in the film due to contamination.
[0010] Embodiments of the present invention may be practiced in the CENTURA
® RP Epi chamber available from Applied Materials, Inc., of Santa Clara, California.
It is contemplated that other chambers, including those available from other manufacturers,
may be used to practice embodiments of the invention.
[0011] Figure 1 is a flow chart 100 illustrating a method of forming a phosphorus-containing
silicon epitaxial layer. In step 102, a monocrystalline silicon substrate is positioned
within a processing chamber. In step 104, the substrate is heated to a predetermined
temperature. The substrate is generally heated to a temperature within a range from
about 550 degrees Celsius to about 700 degrees Celsius. It is desirable to minimize
the thermal budget of the final device by heating the substrate to the lowest temperature
sufficient to thermally decompose process reagents and deposit an epitaxial film on
the substrate. However, as increased temperatures generally lead to increased throughput,
it is contemplated that higher temperatures may be used as dictated by production
requirements.
[0012] In step 106, process gases containing processing reagents are introduced into the
processing chamber. The process gases include a silicon source and phosphorus source
for depositing a phosphorus-containing silicon epitaxial layer on the substrate. The
process gases also include a carrier gas for delivering the silicon source and the
phosphorus source to the processing chamber, as well as an etchant when performing
selective deposition processes.
[0013] The phosphorus source includes phosphine, which source is delivered to the processing
chamber at a rate of about 2 sccm to about 30 sccm. For example, the flow rate of
phosphine may be about 12 sccm to about 15 sccm. Suitable carrier gases include nitrogen,
hydrogen, or other gases which are inert with respect to the deposition process. The
carrier gas is be provided to the processing chamber at a flow rate within a range
from about 3 SLM to about 30 SLM. Suitable silicon sources include dichlorosilane,
silane, and disilane. The silicon source is delivered to the processing chamber at
a flow rate between about 300 sccm and 400 sccm. While other silicon and phosphorus
sources are contemplated, it is generally desirable that carbon addition to the processing
atmosphere is minimized, thus, carbon-containing precursors should be avoided.
[0014] In step 108, the mixture of reagents is thermally driven to react and deposit a phosphorus-containing
silicon epitaxial layer on the substrate surface. During the deposition process, the
pressure within the processing chamber is maintained at 39996.7 Pa (300 Torr) or greater,
for example, 39996.7 Pa to 79993.4 Pa (300 Torr to 600 Torr). It is contemplated that
pressures greater than about 79993.4 Pa (about 600 Torr) may be utilized when low
pressure deposition chambers are not employed. In contrast, typical epitaxial growth
processes in low pressure deposition chambers maintain a processing pressure of about
1333.22 Pa to about 13332.2 Pa (about10 Torr to about 100 Torr) and a processing temperature
greater than 700 degrees Celsius. However, by increasing the pressure to about 19998.4
Pa (about 150 Torr) or greater, the deposited epitaxial film is formed having a greater
phosphorus concentration (e.g., about 1 ×10
21 atoms per cubic centimeter to about 5×10
21 atoms per cubic centimeter) compared to lower pressure epitaxial growth processes.
Furthermore, high flow rates of phosphorus source gas provided during low pressure
depositions often result in "surface poisoning" of the substrate, which suppresses
epitaxial formation. Surface poisoning is typically not experienced when processing
at pressures above 39996.7 Pa (300 Torr), due to the silicon source flux overcoming
the poisoning effect. Thus, increased processing pressures are desirable for epitaxial
processes utilizing high dopant flow rates.
[0015] In a non-claimed example, the phosphorus concentration of an epitaxial film formed
at a pressure less than 13332.2 Pa (100 Torr) is approximately 3×10
20 atoms per cubic centimeter when providing a phosphine flow rate of about 3 sccm to
about 5 sccm. Thus, epitaxial layers formed at higher pressures (e.g., 39996.7 Pa
(300 Torr) or greater) experience approximately a tenfold increase in phosphorus concentration
compared to epitaxial films formed at pressures below about 13332.2 Pa (about 100
Torr) or less. It is believed that at a phosphorus concentration of about 1 ×10
21 atoms per cubic centimeter or greater, the deposited epitaxial film is not purely
a silicon film doped with phosphorus, but rather, that the film is an alloy between
silicon and silicon phosphide (e.g., pseudocubic Si
3P
4). It is believed that the silicon/silicon phosphide alloy attributes to the increased
tensile stress of the epitaxial film. The likelihood of forming the silicon/silicon
phosphide alloy increases with greater phosphorus concentrations, since the probability
of adjacent phosphorus atoms interacting is increased.
[0016] Epitaxial films which are formed at process temperatures between about 550 degrees
Celsius and about 750 degrees Celsius and at pressures above 39996.7 Pa (300 Torr)
experience increased tensile stress when doped to a sufficient phosphorus concentration
(e.g., about 1 ×10
21 atoms per cubic centimeter or greater). Carbon- free epitaxial films formed under
such conditions experience approximately 1 gigapascal to about 1.5 gigapascals of
tensile stress, which is equivalent to a low pressure silicon epitaxial film containing
about 1.5 percent carbon. However, as noted above, epitaxial films containing greater
than about 1 percent carbon suffer from decreased film quality, and are thus undesirable.
Furthermore, carbon-doped silicon epitaxy processes typically utilize cyclical deposition-etch
processes which increase process complexity and cost. Producing an epitaxial film
according to embodiments herein not only results in a film having a tensile stress
equal to or greater than a 1 .5 percent carbon-containing epitaxial film, but the
resistivity of the carbon-free film is also lower (e.g., about 0.6 milliohm-centimeters
compared to about 0.9 milliohm-centimeters). Thus, the substantially carbon-free epitaxial
film exhibits higher film quality, lower resistivity, and equivalent tensile stress
when compared to carbon-containing epitaxial films.
[0017] The tensile strain of the epitaxially-grown film can further be increased by reducing
the deposition temperature during the epitaxial growth process. In a first example
according to the claimed invention, a phosphorus-doped silicon epitaxial film is deposited
at a chamber pressure of 93325,7 Pa (700 Torr) and a temperature of about 750 degrees
Celsius. Process gases containing 300 sccm of dichlorosilane and 5 sccm of phosphine
were provided to a process chamber during the growth process. The deposited film contained
a phosphorus concentration of about 3×10
20 atoms per cubic centimeter, and exhibited a tensile strain equal to a silicon epitaxial
film having a carbon concentration of about 0.5 atomic percent. In a second example
according to the invention, a phosphorus- doped silicon epitaxial film was deposited
on another substrate under similar process conditions; however, the process temperature
was reduced to about 650 degrees Celsius, and the flow rate of phosphine was increased
to 20 sccm. The phosphorus-doped silicon epitaxial film had a tensile strain equivalent
to a film containing 1.8 atomic percent carbon. Thus, as process temperature is reduced
and dopant concentration is increased, the tensile strain within the deposited epitaxial
film increases. It is to be noted, however, that the tensile strain benefits due to
decreased temperature may be limited, since there is minimum temperature which is
required to react and deposit the process reagents.
[0018] In a third example according to the invention, a phosphorus-doped silicon epitaxial
film was formed under similar process conditions as the first example; however, the
flow rate of phosphine during processing was reduced to about 2 sccm. The resultant
phosphorus-doped silicon epitaxial film had a tensile strain equivalent to a film
having about 0.2 percent carbon. Additionally, the resultant film had a resistivity
of about 0.45 milliohm-centimeters compared to 0.60 milliohm-centimeters for the film
of the first example. Thus, not only can the tensile strain of an epitaxial film be
adjusted by varying temperature and or pressure during the deposition process, but
the resistivity can also be adjusted by varying the amount of dopant provided to the
processing chamber.
[0019] Figure 2 is a graph illustrating the dopant profile of a film formed according to
embodiments of the invention. The analyzed film of Figure 2 was formed by heating
a silicon substrate having a silicon-germanium layer thereon to a temperature of about
650 degrees Celsius. Approximately 300 sccm of dichlorosilane and 30 sccm of phosphine
were delivered to a processing chamber maintained at a pressure of about 79993.4 Pa
(about 600 Torr). A 450 angstrom silicon epitaxial film was formed on the silicon-germanium
layer. As determined by secondary ion mass spectroscopy, the phosphorus-doped epitaxial
film had a uniform phosphorus concentration of about 3×10
21 atoms per cubic centimeter, and was substantially free of carbon. In contrast to
the film analyzed in Figure 2, epitaxial films formed at lower pressures, such as
less than 39996.7 Pa (300 Torr), have a phosphorus concentration of about 3×10
20 atoms per cubic centimeter. Thus, the epitaxial film formed according to embodiments
described herein exhibited a tenfold increase in phosphorus concentration as compared
to epitaxial films formed at lower pressures.
[0020] Figure 3 is a graph illustrating the tensile stress of the film of Figure 2 as determined
by high resolution X-ray diffraction. The peak A corresponds to the tensile stress
of the monocrystalline silicon substrate, while the peak B corresponds to the tensile
stress of the silicon-germanium layer. The peak C corresponds to the tensile stress
of the phosphorus-containing epitaxial layer. The well defined edges of the peak B
and the peak C are indicative of high quality epitaxial films having uniform composition.
The peak B corresponds to a silicon-germanium epitaxial layer containing about 12.3
percent germanium. The peak B has a shift between about -1000 arc seconds and about
-1500 arc seconds (e.g., compressed stress), and an intensity of about 1000 a.u. The
peak C has a peak shift of about 1700 arc seconds to about 2400 arc seconds (e.g.,
tensile stress), and an intensity of about 800 a.u. The stress corresponding to peak
C is similar to that of an epitaxial film having a carbon concentration of about 1.8
atomic percent. As discussed above, epitaxial films containing greater than about
1 atomic percent carbon have unacceptable film quality. Thus, while the tensile strength
of highly phosphorus-doped epitaxial films is about equal to an epitaxial film containing
1.8 atomic percent carbon, the highly phosphorus-doped epitaxial films exhibit a higher
film quality than the carbon-doped epitaxial films of comparable tensile strain.
[0021] Benefits of the invention include high quality silicon epitaxial films exhibiting
high tensile strain. Increased process pressures combined with reduced process temperatures
allow for formation of a silicon epitaxial film having a phosphorus concentration
of 3×10
21 atoms per cubic centimeter or greater, without experiencing surface poisoning. The
high phosphorus concentration induces stress within the deposited epitaxial film,
thereby increasing tensile strain, leading to increased carrier mobility and improved
device performance. The tensile strain obtained by highly phosphorus-doped epitaxial
silicon is comparable to epitaxial films containing up to 1.8 atomic percent carbon.
However, highly phosphorus-doped epitaxial silicon of the present invention avoids
the quality issues associated with carbon-doped films.
[0022] While the foregoing is directed to embodiments of the present invention, other and
further embodiments of the invention may be devised without departing from the basic
scope thereof, and the scope thereof is determined by the claims that follow.
1. A method (100) of forming a film on a substrate, comprising:
positioning (102) a substrate within a processing chamber;
heating (104) the substrate to a temperature within a range from 550 degrees Celsius
to 750 degrees Celsius;
introducing (106) process gases into the processing chamber, the process gases comprising
a silicon source, a phosphorus source including phosphine, and a carrier gas, wherein
the silicon source is introduced at a gas flow rate between 300 sccm to 400 sccm,
the phosphorus source is introduced at a gas flow rate between 2 sccm to 30 sccm,
and the carrier gas is introduced at a gas flow rate of 3 to 30 standard liter per
minute; and
depositing (108) a substantially carbon-free epitaxial layer on the substrate, the
substantially carbon-free epitaxial layer having a phosphorus concentration of 1×1021 atoms per cubic centimeter or greater, wherein the substantially carbon-free epitaxial
layer is deposited at a chamber pressure of 39996.7 Pa (300 Torr) or greater.
2. The method of claim 1, wherein the silicon source is dichlorosilane.
3. The method of claim 2, wherein the phosphorus source is phosphine.
4. The method of claim 1, wherein the temperature is within a range from 600 degrees
Celsius to 650 degrees Celsius.
5. The method of claim 4, wherein the silicon source is silane or disilane.
1. Verfahren (100) zum Bilden einer Folie auf einem Substrat, umfassend:
Positionieren (102) eines Substrats innerhalb einer Verarbeitungskammer;
Erwärmen (104) des Substrats auf eine Temperatur innerhalb eines Bereichs von 550
Grad Celsius bis 750 Grad Celsius;
Einleiten (106) von Prozessgasen in die Verarbeitungskammer, wobei die Prozessgase
eine Siliziumquelle, eine Phosphorquelle einschließlich Phosphin und ein Trägergas
umfassen, wobei die Siliziumquelle bei einer Gasdurchflussmenge zwischen 300 sccm
und 400 sccm eingeleitet wird, die Phosphorquelle mit einer Gasdurchflussmenge zwischen
2 sccm und 30 sccm eingeleitet wird und das Trägergas bei einer Gasdurchflussmenge
von 3 bis 30 Standardliter pro Minute eingeleitet wird; und
Abscheiden (108) einer im Wesentlichen kohlenstofffreien Epitaxieschicht auf dem Substrat,
wobei die im Wesentlichen kohlenstofffreie Epitaxieschicht eine Phosphorkonzentration
von 1 × 1021 Atomen pro Kubikzentimeter oder höher aufweist, wobei die im Wesentlichen kohlenstofffreie
Epitaxieschicht bei einem Kammerdruck von 39996,7 Pa (300 Torr) oder höher abgeschieden
wird.
2. Verfahren nach Anspruch 1, wobei die Siliziumquelle Dichlorsilan ist.
3. Verfahren nach Anspruch 2, wobei die Phosphorquelle Phosphin ist.
4. Verfahren nach Anspruch 1, wobei die Temperatur innerhalb eines Bereichs von 600 Grad
Celsius bis 650 Grad Celsius liegt.
5. Verfahren nach Anspruch 4, wobei die Siliziumquelle Silan oder Disilan ist.
1. Procédé (100) de formation d'un film sur un substrat, comprenant :
le positionnement (102) d'un substrat à l'intérieur d'une chambre de traitement ;
le chauffage (104) du substrat à une température dans la plage de 550 degrés Celsius
à 750 degrés Celsius ;
l'introduction (106) de gaz de traitement dans la chambre de traitement, les gaz de
traitement comprenant une source de silicium, une source de phosphore contenant de
la phosphine, et un gaz porteur, dans laquelle la source de silicium est introduite
à un débit de gaz compris entre 300 Ncm3/min et 400 Ncm3/min, la source de phosphore est introduite à un débit de gaz compris entre 2 Ncm3/min et 30 Ncm3/min, et le gaz porteur est introduit à un débit de gaz de 3 à 30 normo-litres par
minute ; et
la déposition (108) d'une couche épitaxiale sensiblement exempte de carbone sur le
substrat, la couche épitaxiale sensiblement exempte de carbone ayant une concentration
de phosphore de 1 × 1021 atomes par centimètre cube ou plus, dans laquelle la couche épitaxiale sensiblement
exempte de carbone est déposée sous une pression de chambre de 39996,7 Pa (300 Torr)
ou plus.
2. Procédé selon la revendication 1, dans lequel la source de silicium est le dichlorosilane.
3. Procédé selon la revendication 2, dans lequel la source de phosphore est la phosphine.
4. Procédé selon la revendication 1, dans lequel la température est dans la plage de
600 degrés Celsius à 650 degrés Celsius.
5. Procédé selon la revendication 4, dans lequel la source de silicium est le silane
ou le disilane.